This year, several stalwart members of the Democratic caucus will write the final chapter in their Senate careers.

Even if Democrats hold control of the Senate in 2015, the chamber will be a different place, with five chairmen set to retire at the end of the 113th Congress. These senators are among the last connections to the “Old Bulls” who steered their committees in the past, having about 150 years of combined service.

But some of the retiring senators are hopeful that a bit of the relatively new blood will reinvigorate the environment.

Asked how new chairmen might change the place, outgoing Armed Services Chairman Carl Levin of Michigan replied, "Hopefully for the better. I'm always an optimist. There's room for improvement in this place."

In a sign of how much is changing quickly, a number of the new Old Bulls are women. Budget Chairwoman Patty Murray of Washington and Appropriations Chairwoman Barbara A. Mikulski of Maryland have led their caucus in recent budget negotiations, and Sen. Debbie Stabenow of Michigan continues to lead efforts to complete a farm bill.

Republicans go through the process of changing committee leaders far more frequently, because their conference has six-year term limits for chairmen and ranking members, a point made by Senate Historian Emeritus Richard A. Baker.

“Usually the rising chairmen and women also have been around awhile and, by virtue of their own seniority, ease the transitions,” Baker said in an email. “The obvious losers are the states represented by the departing chairs.”

Former Sen. Ted Kaufman, a longtime Senate aide who took the seat vacated by his former boss, Joseph R. Biden Jr. of Delaware, noted that there's been huge turnover in the chairman ranks in recent years.

"The good news is that I am very impressed with the newer members who will become chairs if the Democrats hold on to control of the Senate. They are among the best that I have seen in my 40 years," Kaufman said. "The bad news is that being chair is a very complex position, and because the Senate relies so much on precedent, institutional memory is very important. There will be a learning process."

The retiring senators expect their understudies will be prepared for the leading roles.

"What people constantly overlook is the fact that right underneath a bunch of us is a bunch of absolutely superbly trained people who're ready to take over," said Rockefeller, who was first elected in 1984.

He called the prospective successors “very, very good members, and so we lose a little experience but no knowledge and no fortitude."

Like Rockefeller at the Commerce Committee, his classmate Tom Harkin of Iowa will yield the gavel of the Health, Education, Labor and Pensions Committee.

"It represents opportunities for a lot of Democrats to move up and take positions of ... responsibility and leadership, so it's a good thing," Harkin said. "It's time to get younger people moving up the ladder."

Of course, the successors won’t exactly be spring chickens. The anticipated Baucus confirmation to the China posting would clear the way for Oregon Democrat Ron Wyden to be Finance chairman.

Wyden’s been in the Senate since winning a 1996 special election to fill the seat vacated when Republican Bob Packwood, another Finance chairman, resigned in disgrace. To put this in perspective: When Packwood resigned, Baucus was already second in seniority among panel Democrats behind only Daniel Patrick Moynihan of New York.

In the meantime, the retiring chairmen don’t plan on going away quietly. Harkin and Rockefeller have both taken passes on traditionally more plum assignments than their current roles due to unexpected vacancies late in their final terms. Rockefeller has said he won’t assert seniority on Finance, and Harkin opted against pursuing the chairmanship of the Appropriations Committee, helping hand it to Mikulski when it was vacated after the death of Daniel K. Inouye, D-Hawaii.

"I love my committee. I like the HELP Committee. I had some ... irons in the fire … that I wanted to work on before I left the Senate,” Harkin said. “That's where my interest was.”

That arrangement seems to have worked out pretty well. Harkin praised Mikulski’s leadership of the spending panel, marveling at her ability to get House Republicans to agree to include a full Labor-HHS-Education spending measure in the recent fiscal 2014 omnibus. Harkin’s the chairman of that Senate subcommittee.

As for the HELP agenda, Harkin rattled off a perhaps overly aggressive list of big-ticket items he would like to advance before retirement at the beginning of January 2015, noting he might be missing something.

"I've got the Workforce Investment Act that I've worked very hard on [that] I hope to bring on the floor here sometime soon. Minimum wage, the Elementary and Secondary Education Act, the Higher Education Act ... those are the big ones that I've been working on," Harkin said.

The ESEA reauthorization has been better known recently as No Child Left Behind.

The No. 1 priority for Levin, the retiring Armed Services chairman, will be the same as in any other year: completing work on the annual defense authorization bill. But when asked about other plans, Levin was quick to point to his work investigating tax avoidance strategies such as offshore tax havens. Levin said to expect more of that in 2014, calling "identifying ... unjustified tax loopholes” his second priority.

But Kaufman doubts that Levin and the other chairmen retiring this year might get the customary chance for "legacy" legislation.

"It is unfortunate that, with the makeup of the Senate and especially the attitude of a number of the new senators, I do not believe that will be happening in this Congress," Kaufman said.

Still, no one should be too surprised to see a "Carl Levin National Defense Authorization Act" emerge by year's end.